The champions capitalised on slip ups by nearest challengers Chelsea and Liverpool by beating Brentford 1-0 on Wednesday.
Phil Foden’s 16th minute strike at the Brentford Community stadium gave City all three points and extend their winning run in the top flight to 10 matches.
"We won the game, we are on a good run, but it's the end of December,” Guardiola said after the game.
"There are many games to go. We are eight points in front but there are 54 still to play for and many tough games still to play.
"I'm not going to believe anyone who says it's already done. The teams we have with Chelsea and Liverpool are more than exceptional.
"We have the distance not because they dropped points but because we won 10 in a row. But there are 54 points still to play for."
Guardiola added on City goalscorer Foden, who was restored to the starting 11 after being dropped for their recent wins over Newcastle United and Leicester City because of indiscipline: "Phil has always been outstanding. He's a guy who can play in different positions at an exceptional level.
"We had no doubts about that. Did he have anything to prove? Absolutely not."
City return to action on New Year’s Day with a trip to Arsenal.
